Cationic polymerization of styrenes by protonic acids and their derivatives, 4. Homo‐ and Co‐polymerizations of <i>para</i>‐substituted styrenes by CF₃SO₃H

<jats:title>Abstract</jats:title><jats:p><jats:italic>p</jats:italic>‐Methyl‐ and <jats:italic>p</jats:italic>‐chlorostyrenes (pMeSt and pClSt) were polymerized by CF<jats:sub>3</jats:sub>SO<jats:sub>3</jats:sub>H in methylene chloride at 0°C and gave polymers with a bimodal molecular weight distribution (MWD). This indicates that the polymerizations involve two independent propagating species: a dissociated and a non‐dissociated species. Their selectivities toward monomers were compared in the copolymerizations of pMeSt and pClSt with styrene (St) by CF<jats:sub>3</jats:sub>SO<jats:sub>3</jats:sub>H in benzene, methylene chloride, and nitrobenzene solvents. Decreasing solvent polarity and the presence of a common‐ion salt ((<jats:italic>n</jats:italic>‐C<jats:sub>4</jats:sub>H<jats:sub>9</jats:sub>)<jats:sub>4</jats:sub>N<jats:sup>+</jats:sup>SO<jats:sub>3</jats:sub>CF<jats:sup>−</jats:sup><jats:sub>3</jats:sub>) greatly increased the reactivity difference between the monomers. Thus the non‐dissociated species is more selective than the dissociated species. In contrast, the composition of pMeSt‐St copolymers produced by BF<jats:sub>3</jats:sub>O(C<jats:sub>2</jats:sub>H<jats:sub>5</jats:sub>)<jats:sub>2</jats:sub> did not change with the solvent polarity. The difference in nature between the propagating species generated by CF<jats:sub>3</jats:sub>SO<jats:sub>3</jats:sub>H and by BF<jats:sub>3</jats:sub>O(C<jats:sub>2</jats:sub>H<jats:sub>5</jats:sub>)<jats:sub>2</jats:sub> is discussed.</jats:p>